In present-day digital mobile communication systems, user information, i.e. speech and data, are transferred over the radio interface in digital form. In some cases, it is possible to select out of many transfer rates the one which is best suited to a speech coding rate used and to data transfer requirements of the user. The transfer rate is typically chosen at the beginning of a call and maintained unchanged for the duration of the call. In mobile communication systems to come, more flexibility is required at the radio interface for embodying various kinds of services. One of the consequences of this requirement for flexibility is a rapidly varying transfer rate during a call. In a digital mobile communication system, for example, in which user information is packed into transmission frames (10 ms of duration, for example), each frame may have a transfer rate independent of the previous or the subsequent transfer frame. However, a problem emerges in how to transfer information on the current transfer rate as quickly as possibly from the transmitter to the receiver in order for the receiver to be able to adapt its operation to the transfer rate being used. In addition, in interference limited mobile communication systems such as spread spectrum radio systems, it is advantageous to employ a fast closed loop power control. By means of power control, a base stations seeks to adjust the transmit power of mobile stations so that all the signals transmitted by the mobile stations are received by the base station at the same nominal power level. In other words, by means of power control, the aim is to average the energy of a symbol transmitted over the radio path, and therefore the transmit power is also proportional to rate. Due to this, when employing closed loop power control, the receiver needs to know the current transfer rate without delay.
A known solution is to employ on the radio path a separate signalling channel through which information on the transfer rate is conveyed from the transmitter to the receiver. The closed loop power control can be carried out with such a signalling channel. Separate signalling, however, causes delay in the practical implementation. The message indicating transfer rate is protected against interference and interleaved in the transmitter. The most efficient interleaving lasts for the length of the transfer frame. Prior to knowing the transfer rate and completing the user signal processing, deinterleving and error correction are carried out in the receiver. As a consequence the received user signal has to be buffered until these reception operations are completed. A further consequence is that activating the closed loop power control is delayed. If the receiver of a spread spectrum system utilizes interference cancellation (IC) or multiuser detection (MUD), the delay caused by detecting the transfer rate employed also concerns the interfering signals (other users). In an asynchronous spread spectrum mobile communication system, the propagation delay, with the above assumptions, will be twice the interleaving depth+signal processing delay.